1. Technical Field
The present invention relates to a full-bridge driving controller and a full-bridge converting circuit, and more particularly relates to a full-bridge driving controller and a full-bridge converting circuit having the function of soft switch.
2. Description of Related Art
Types of conventional DC to DC converting circuit comprise a step-up converting circuit, a step-down converting circuit, a flyback converting circuit, a forward converting circuit, a half-bridge converting circuit and a full-bridge converting circuit, etc.
FIG. 1 is a schematic diagram of a conventional full-bridge converting circuit. The full-bridge converting circuit comprises a first transistor switch M1, a second transistor switch M2, a third transistor switch M3, a fourth transistor switch M4, a transformer T, a first rectification diode D1, a second rectification diode D2, an inductance L and an output capacitance Co. Each of the first transistor switch M1 and the third transistor switch M3 has one terminal coupled to an input power source VIN and another terminal coupled to two terminals of a primary side of the transformer T respectively. Each of the transistor switch M2 and the fourth transistor switch M4 has one terminal grounded and another terminal coupled to two terminals of the primary side of the transformer T respectively. Two terminals of a secondary side of the transformer T are coupled to the first rectification diode D1 and the second rectification diode D2, thereby storing rectified electric power in the inductance L and the output capacitance Co. The switching operations of the aforementioned four transistor switches M1, M2, M3 and M4 are controlled by a first control signal S1, a second control signal S2, a third control signal S3 and a fourth control signal S4 respectively. FIG. 2 is a schematic switching timing diagram of the transistor switches of the full-bridge converting circuit shown in FIG. 1. A phase of the first control signal S1 is equal to that of the fourth control signal S4, and a phase of the first control signal S2 is also equal to that of the fourth control signal S3. Therefore, the first transistor switch M1 and the fourth transistor switch M4 are turned on at the same time to provide a conduction path from the input power source VIN through the first transistor switch M1, the primary side of the transformer T, and the fourth transistor switch M4 to the ground. At this time, the secondary side of the transformer T generates an induced current flowing from the first transistor D1 through the inductance L to the output capacitance Co, and thus an electric power is stored in the inductance L and the output capacitance Co. When the second transistor switch M2 and the third transistor switch M3 are turned on, another conduction path is also provided from the input power source VIN through the third transistor switch M3, the primary side of the transformer T and the second transistor switch M2 to the ground. At this time, the secondary side of the transformer T generates an induced current flowing through the second transistor D2, the inductance L and the output capacitance Co for storing electric power.
Although a conversion efficiency of the switching converting circuit is high, yet a conduction loss or a switching loss, etc. still occurs in an actual operation. Under the global trend of energy-saving and carbon reduction in the current stage, many countries have legislated energy efficiency regulations or announced energy efficiency certifications, such as 80 plus certification in U.S. The requirements for conversion efficiency in the regulations or certifications are hard to be complied by the conventional converting circuits. Therefore, how to increase the conversion efficiency of the switching converting circuit is one of the most important issues presently.